In the electronics industry there is a growing need for volatile sources of different metals to be used in the chemical vapor deposition (CVD) of metallic films, metal oxide films, metal silicide films, and the like. The key property required for such metal sources is that they readily evaporate or sublime to give a metal containing vapor or gas which can be decomposed in a controlled manner to deposit a film onto a target substrate. Examples of such materials which are commonly utilized in the microelectronics industry in the preparation of printed circuits and semiconductor devices include the complex H.sub.3 SiCo(CO).sub.4 complex which is pyrolyzed in the gas phase at 670.degree.-770.degree. K. to produce CoSi and dimethylzinc (1,4 dioxane) which is reacted with hydrogen selenide at 250.degree.-550.degree. C. to produce ZnSe. References teaching the above CVD methods are B. J. Aylett, et al in Vacuum, 35 p 435-439(1985) and P. J. Wright, et al., in a paper accepted for publication in J. of Crystal Growth, London (1986), respectively.
Known fluorinated metal complexes that are chemically stable and easily volatized into the gas phase are the perfluorinated .beta.-diketone metal coordination compounds along with their parent .beta.-diketone precursor ligands, represented by the formulas: ##STR2## wherein R.sub.1 is alkyl or fluoroalkyl, R.sub.2 is fluoroalkyl, and M is a metal capable of forming a coordination compound. The volatility and gas phase stability of these compounds have been exploited for the gas chromatographic separation of various metals, the purification of uranium and the manufacture of specialty glasses. Decomposing such metal complexes by reaction with hydrogen in the gas phase to deposit thin metal films is taught in U.S. Pat. No. 3,356,527.
In the past, attempts have been made to condense primary amines or primary diamines with ligands similar to those having the above structure. In instances in which R.sub.1 and R.sub.2 are not both fluorocarbon groups, it was reported that an 0 atom could be replaced with a N atom from an amine by direct Schiff-base condensation between an appropriate .beta.-diketone and an amine. Additionally, the corresponding metal complex could be synthesized by chelation to a metal ion. See A. E. Martell, et al J. Inorg. Chem. Vol. 5 pp 170-181 (1958).
As reported by Sievers, et al in J. Inorg. Nucl. Chem. Vol. 32 pp 1895-1906 (1970), ligands in which R.sub.1 and R.sub.2 are both perfluoralkyl and in which an oxygen has been replaced with an amine have not been obtainable. It is believed that such methods have been unsuccessful because the perfluorinated .beta.-diketones are of such high acidity that the amine used in the reaction becomes protonated, thereby forming a salt between the amine and the .beta.-diketone rather than forming the desired ligand. Sievers, et al do report synthesizing a ligand having the structure: ##STR3## wherein R.sub.1 =R.sub.2 =CF.sub.3 and R.sub.3 =--CH.sub.2 CH.sub.2 --. This ligand was reportedly synthesized by sublimation of the salt [(CF.sub.3 C(O)CHC(O)CF.sub.3)].sub.2.sup.-[NH.sub.3 --CH.sub.2 CH.sub.2 NH.sub.3 ].sup.+2. The ligand was reported to be chemically unstable and hence impossible to isolate.
Charles, U.S. Pat. No. 3,594,216 discloses a process for depositing a metallic coating on a substrate by heating the substrate and contacting it with vaporized metal-organic beta-ketoamine chelates. The metal-organic beta-ketoamines were prepared by conventional synthesis techniques. While a wide range of metal chelates are disclosed generally, none of the examples or synthesis techniques specifically use perfluorinated metal chelates.
Johnson, et al in Journal of Fluorine Chemistry, 27 pp 371-378 (1985) reported synthesizing a ligand in which R.sub.1 and R.sub.2 are perfluoroalkyl and oxygen was replaced with an ammonia nitrogen. The Cu.sup.+2 complex was also prepared and was reported to be volatile.